A semiconductor memory device in which a silicon oxide film and a gate insulating film are provided in this order on a p-type silicon substrate is known. Impurities such as Al atoms, Au atoms and Ti atoms are included in the silicon oxide film of the semiconductor memory device. Charges are accumulated in trap sites introduced by the impurities. The semiconductor memory device is disclosed in International Patent Application Publication WO2006-095890.
But in the semiconductor memory device, as Al atoms, Au atoms and Ti atoms diffuse in the silicon oxide, the charges accumulated in the silicon oxide film diffuse. Accordingly, it is difficult to accumulate the charges effectively.